free radical initiator system and a high pressure, freeradical polymerization process for producing a low density polyethylene polymer

ABSTRACT

The instant invention is a free radical initiator system, and a high pressure, free radical polymerization process for producing a low density polyethylene polymer. The free radical initiator system according to instant invention includes at least one peroxide initiator, at least one hydrocarbon solvent, and at least one polar co-solvent. The high pressure, free radical polymerization process for producing a low density polyethylene polymer includes the steps of polymerizing ethylene and optionally at least one comonomer under high pressure conditions using a free radical initiator system comprising at least one peroxide initiator, at least one hydrocarbon solvent, and at least polar co-solvent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application claiming priority fromthe U.S. Provisional Patent Application No. 60/905,999, filed on Mar. 9,2007 entitled “FREE RADICAL INITIATOR SYSTEM AND A HIGH PRESSURE, FREERADICAL POLYMERIZATION PROCESS FOR PRODUCING A LOW DENSITY POLYETHYLENEPOLYMER” the teachings of which are incorporated by reference herein asif reproduced in full hereinbelow.

FIELD OF INVENTION

The instant invention relates to a free radical initiator system, and ahigh pressure, free radical polymerization process for producing a lowdensity polyethylene polymer.

BACKGROUND OF THE INVENTION

The use of peroxide initiators in high pressure free radicalpolymerization of ethylene and optionally at least one comonomer isgenerally known. As a general rule, peroxide initiators need to bestored at relatively low temperatures of less than 30° C. to −20° C. inorder to prevent premature decomposition. For metering into thepolymerization reactor by means of piston pumps and other injectionequipment, the peroxide initiators are typically dissolved or diluted ina hydrocarbon solvent. However, the solubility of peroxide initiatorsare affected by pressure conditions and/or composition conditionsexperienced in the peroxide storage, and injection and metering systems.As a result, a phase separation, e.g. liquid-liquid phase separation orsolid-liquid phase separation, may occur. The phase separation ofperoxide/solvent mixture may interrupt its injection into thepolymerization reactor or it may cause a non-uniform peroxideconcentration. A stable initiator/solvent mixture having a uniforminitiator concentration is an important requirement to achieve a stablehigh pressure free radical polymerization process and to avoid ethylenedecomposition in high pressure low density polyethylene reactors.

U.S. Pat. No. 3,642,747 discloses the production of ethylenehomopolymers or copolymers by polymerization of ethylene or of mixturesof major amounts of ethylene and minor amounts of other monomers atsuper-atmospheric pressure and elevated temperature using apolymerization initiator. It is characteristic of the process accordingto the invention that a 2-hydro-peroxy-2-isopropylphenylpropane is usedas polymerization initiator.

U.S. Pat. No. 3,714,135 discloses the production of homopolymers orcopolymers of ethylene by homopolymerization of ethylene orcopolymerization of mixtures of ethylene and other monomers atsuper-atmospheric pressure and elevated temperature under the influenceof a free radical generating polymerization initiator with or without apolymerization regulator. The initiator used is a mixture of (a) aninitiator having a half-life of ten to 30 hours at 50° C., and (b) aninitiator having a half-life of 0.2 to 10 hours at 50° C., the half-lifeat 50° C. of initiator (a) being at least twice as long as that ofinitiator (b).

U.S. Pat. No. 4,581,429 discloses a processes for free radicalpolymerization, in which it is possible to control the growth steps ofthe polymerization to produce relatively short chain length homopolymersand copolymers, including block and graft copolymers.

U.S. Pat. No. 4,777,230 discloses a process for the free radicalpolymerization of monomers derived from substituted or unsubstitutedacrylic acid/methacrylic acid and esters thereof for the production of apolymer having a narrow molecular weight distribution and an averagemolecular weight of less than 4000. These polymers are produced by thesolution polymerizing of said monomers wherein 20 to 40 percent byweight of the monomer composition is hydroxyalkyl acrylate ormethacrylate in the presence of a solvent system suitable for highsolids coating applications and in the presence of an initiating amountof a tertiary alkyl hydroperoxide and/or its derivatives having at least5 carbons wherein the initiator and monomers, alone or in combination,are added continuously at a programmed rate wherein the rate of additioncorresponds approximately to the rate of decomposition of said monomerand initiator.

U.S. Pat. No. 5,100,978 discloses polyethylene and copolymers ofpredominant amounts of ethylene and minor amounts of comonomers that arepolymerizable with ethylene, obtainable by free radical polymerizationof the monomers under from 1,500 to 5,000 bar and at from 40° C. to 250°C. by means of an initiator with virtually complete exclusion of oxygenin not less than n=3 polymerization stages.

U.S. Pat. No. 5,322,912 discloses a free radical polymerization processfor the preparation of a thermoplastic resin or resins comprisingheating a mixture of a free radical initiator, a stable free radicalagent, and at least one polymerizable monomer compound to form athermoplastic resin or resins with a high monomer to polymer conversion;cooling the mixture; optionally isolating the thermoplastic resin orresins; and optionally washing and drying thermoplastic resin or resins.

U.S. Pat. No. 6,407,191 discloses a free radical initiationpolymerization process for the preparation of medium density ethylenepolymers or copolymers, comprising reacting ethylene and optionally oneor more comonomers at a high pressure, conveniently between 1600 and4000 kg/cm², and at temperatures of about 150-330° C. in a reactorsystem consisting of at least one autoclave reactor or of a combinationof autoclave and tubular reactors, in the presence of free radicalinitiators and a carbonyl group containing compound.

U.S. Pat. No. 6,569,962 discloses a method for producing ethylenehomopolymerizates and ethylene copolymerizates in tubular reactors inthe presence of radical-forming initiators, oxygen thereunder and chaintransfer agents, of which at least one comprises an aldehydic structure.

U.S. Pat. No. 6,727,326 discloses a method for the continuous productionof ethylene homo-polymers and ethylene co-polymers in the presence ofradical polymerization initiators and, optionally, molecular weightregulators in a tubular reactor with a hot water jacket and one orseveral reaction zones at pressures of 1000 to 4000 bar and temperaturesof 120° C. to 350° C.

European Patent No. EP 0221610 discloses a storageable and/ortransportable composition containing a peroxydicarbonate.

European Patent No. EP 0879224 discloses poly(monoperoxycarbonate)compounds and their use as free-radical initiators for polymerizingethylenically unsaturated monomers, such as styrene, at fasterproduction rates while retaining polymer molecular weight and polymerphysical properties.

International Publication No. WO 02/051802 discloses a method to safelyproduce, handle and transport packaged organic peroxide formulationscomprising a reactive phlegmatiser and to the use of such packagedmaterial in polymerization and polymer modification processes,particularly the high-pressure (co)polymerization process of ethyleneand/or the suspension (co)polymerization process of styrene.

International Publication No. WO 2004/052877 discloses a cyclic ketoneperoxide formulation comprising one or more crystallizing cyclic ketoneperoxides, one or more co-crystallizing compounds which solidify in saidcyclic ketone peroxide formulation at a temperature above thecrystallization temperature of the crystallizing cyclic ketone peroxide,and, optionally, one or more conventional phlegmatisers.

International Publication No. WO 2005/092966 discloses the use of acomposition consisting of a crosslinking agent and anefflorescence-inhibiting agent, wherein said crosslinking agent isselected from a group formed by (a) an aromatic peroxide and (b) thecombination of at least of one type aromatic peroxide and at least onetype of aliphatic peroxide and said efflorescence-inhibiting agent beingan alcohol. The efflorescence-inhibiting agent is embodied in the formof a sorbitol, mannitol, glycerol and a polyglycerol or the derivativesthereof.

Despite the research efforts in developing free radical initiatorsystems for high pressure (co)polymerization process, there is still aneed for a stable initiator/solvent mixture having a uniform initiatorconcentration thereby facilitating a stable high pressure free radical(co)polymerization process and avoiding ethylene decomposition in suchhigh pressure low density polyethylene reactors.

SUMMARY OF THE INVENTION

The instant invention is a free radical initiator system, and a highpressure, free radical polymerization process for producing a lowdensity polyethylene polymer. The free radical initiator systemaccording to instant invention includes at least one peroxide initiator,at least one hydrocarbon solvent, and at least one polar co-solvent. Thehigh pressure, free radical polymerization process for producing a lowdensity polyethylene polymer includes the steps of polymerizing ethyleneand optionally at least one comonomer under high pressure conditionsusing a free radical initiator system comprising at least one peroxideinitiator, at least one hydrocarbon solvent, and at least polarco-solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is exemplary; it being understood, however, thatthis invention is not limited to the precise arrangements andinstrumentalities shown.

FIG. 1 is an illustrative diagram of a high pressure optical cell;

FIG. 2 is a graph illustrating the liquid-liquid phase separation as afunction of temperature and pressure for comparative sample solution 1(containing 20 weight percent Luperox JWEB50 and 80 weight percentiso-octane), and inventive sample solution 2 (containing 20 weightpercent Luperox JWEB50 and 10 weight percent isopropanol and 70 weightpercent iso-octane);

FIG. 3 is a graph illustrating the liquid-liquid phase separation as afunction of temperature and pressure for comparative sample solution 3(containing 40 weight percent Luperox JWEB50 and 60 weight percentn-octane), inventive sample solution 4 (containing 40 weight percentLuperox JWEB50 and 5 weight percent isopropanol and 55 weight percentn-octane), and inventive sample solution 5 (containing 40 weight percentLuperox JWEB50 and 10 weight percent isopropanol and 50 weight percentn-octane). FIG. 3 is a graph further illustrating the solid-liquid phaseseparation as a function of temperature and pressure for comparativesample solution 6 (containing 100 weight percent n-octane), andinventive sample solution 7 (containing 40 weight percent Luperox JWEB50and 20 weight percent isopropanol and 40 weight percent n-octane;

FIG. 4 is a graph illustrating the liquid-liquid phase separation as afunction of temperature and pressure for comparative sample solution 8(containing 40 weight percent Luperox JWEB50 and 60 weight percentIsopar E), and inventive sample solution 9 (containing 40 weight percentLuperox JWEB50 and 5 weight percent isopropanol, and 55 weight percentIsopar E);

FIG. 5 is a graph illustrating the liquid-liquid phase separation as afunction of temperature and pressure for comparative sample solution 6(containing 100 weight percent n-octane), comparative sample solution 8(containing 40 weight percent Luperox JWEB50 and 60 weight percentn-octane), inventive sample solution 10 (containing 40 weight percentLuperox JWEB50 and 10 weight percent 1-pentanol and 50 weight percentn-octane); FIG. 5 is a graph further illustrating the solid-liquid phaseseparation as a function of temperature and pressure for comparativesample solution 6 (containing 100 weight percent n-octane), andinventive sample solution 10 (containing 40 weight percent LuperoxJWEB50 and 10 weight percent 1-pentanol and 50 weight percent n-octane);

FIG. 6 is a graph illustrating the liquid-liquid phase separation as afunction of temperature and pressure for comparative sample solution 11(containing 20 weight percent tert-butyl peroxyperacetate (“TBPA”) and80 weight percent iso-dodecane), and inventive sample solution 12(containing 20 weight percent TBPA and 10 weight percent isopropanol and70 weight percent iso-dodecane);

FIG. 7 is a graph illustrating the liquid-liquid phase separation as afunction of temperature and pressure for comparative sample solutions11, 13 and 14 (containing 20 weight percent, 35 weight percent, and 50weight percent TBPA in iso-dodecane, respectively), and for inventivesample solutions 12, 15 and 16 (containing 20 weight percent, 35 weightpercent, and 45 weight percent TBPA with 10 weight percent isopropanolin iso-dodecane, respectively); and

FIG. 8 is a graph illustrating the T-X plot for Trigonox-F at 3different pressure levels, i.e. 500 bar, 1500 bar and 2500 bar, forcomparative sample solutions 11, 13 and 14 (containing 20 weightpercent, 35 weight percent, and 50 weight percent TBPA in iso-dodecane,respectively), and for inventive sample solutions 12, 15 and 16(containing 20 weight percent, 35 weight percent, and 45 weight percentTBPA with 10 weight percent isopropanol in iso-dodecane, respectively).

DETAILED DESCRIPTION OF THE INVENTION

The free radical initiator system according to instant inventionincludes at least one peroxide initiator, at least one hydrocarbonsolvent, and at least one polar co-solvent.

The free radical initiator system includes at least one peroxideinitiator. The peroxide initiator may, for example, be an organicperoxide. Exemplary organic peroxides include, but are not limited to,cyclic peroxides, diacyl peroxides, dialkyl peroxides, hydroperoxides,peroxycarbonates, peroxydicarbonates, peroxyesters, and peroxyketals.

Exemplary cyclic peroxides include, but are not limited to,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane. Such cyclicperoxides, for example, are commercially available under the tradenameTRIGONOX 301, from Akzo Nobel, Arnhem, The Netherlands.

Exemplary diacyl peroxides include, but are not limited to,di(3,5,5-trimethylhexanoyl) peroxide. Such diacyl peroxides, forexample, are commercially available under the tradename TRIGONOX 36,from Akzo Nobel, Arnhem, The Netherlands.

Exemplary dialkyl peroxides include, but are not limited to,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane;2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3; di-tert-amyl peroxide;di-tert-butyl peroxide; and tert-butyl cumyl peroxide. Such dialkylperoxides, for example, are commercially available under the tradenamesTRIGONOX 101, TRIGONOX 145, TRIGONOX 201, TRIGONOX B, and TRIGONOX Tfrom Akzo Nobel, Arnhem, The Netherlands.

Exemplary hydroperoxides include, but are not limited to, tert-Amylhydroperoxide; and 1,1,3,3-tetramethylbutyl hydroperoxide. Suchhydroperoxides, for example, are commercially available under thetradenames TRIGONOX TAHP, and TRIGONOX TMBH, from Akzo Nobel, Arnhem,The Netherlands.

Exemplary peroxycarbonates include, but are not limited to,tert-butylperoxy 2-ethylhexyl carbonate; tert-amylperoxy 2-ethylhexylcarbonate; and tert-butylperoxy isopropyl carbonate. Suchperoxycarbonates, for example, are commercially available under thetradenames TRIGONOX 117, TRIGONOX 131, and TRIGONOX BPIC, from AkzoNobel, Arnhem, The Netherlands.

Exemplary peroxydicarbonates include, but are not limited to,di(2-ethylhexyl) peroxydicarbonates; and di-sec-butylperoxydicarbonates. Such peroxydicarbonates, for example, arecommercially available under the tradename TRIGONOX EHP, and TRIGONOXSBP, from Akzo Nobel, Arnhem, The Netherlands.

Exemplary peroxyesters include, but are not limited to, tert-amylperoxy-2-ethylhexanoate; tert-amyl peroxyneodecanoate; tert-amylperoxypivalate; tert-amyl peroxybenzoate; tert-amyl peroxyacetate;2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane; tert-butylperoxy-2-ethylhexanoate; tert-butyl peroxyneodecanoate; tert-butylperoxyneoheptanoate; tert-butyl peroxypivalate; tert-butylperoxydiethylacetate; tert-butyl peroxyisobutyrate;1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate;1,1,3,3-tetramethylbutyl peroxyneodecanoate; 1,1,3,3-tetramethylbutylperoxypivalate; tert-butyl peroxy-3,5,5-trimethylhexanoate; cumylperoxyneodecanoate; tert-butyl peroxybenzoate; and tert-butylperoxyacetate. Such peroxyesters solvents, for example, are commerciallyavailable under the tradenames TRIGONOX 121; TRIGONOX 123; TRIGONOX 125;TRIGONOX 127; TRIGONOX 133; TRIGONOX 141; TRIGONOX 21; TRIGONOX 23;TRIGONOX 257; TRIGONOX 25; TRIGONOX 27; TRIGONOX 41; TRIGONOX 421;TRIGONOX 423; TRIGONOX 425;TRIGONOX 42; TRIGONOX 99; TRIGONOX C; andTRIGONOX F, from Akzo Nobel, Arnhem, The Netherlands.

Exemplary peroxyketals include, but are not limited to,1,1-di(tert-amylperoxy)cyclohexane; 1,1-di(tert-butylperoxy)cyclohexane;1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane; and2,2-di(tert-butylperoxy)butane. Such peroxyketals, for example, arecommercially available under the tradenames TRIGONOX 122, TRIGONOX 22,TRIGONOX 29, and TRIGONOX D, from Akzo Nobel, Arnhem, The Netherlands.

The free radical initiator system may, for example, include a mixture orcombination of any of the above mentioned peroxide initiators.

The free radical initiator system may, for example, comprise less than60 percent by weight of the peroxide initiator, based on the weight ofthe free radical initiator system. All individual values and subrangesless than 60 weight percent are included herein and disclosed herein;for example, the free radical initiator system may comprise 1 to 40percent by weight of the peroxide initiator, based on the weight of thefree radical initiator system; or in the alternative, the free radicalinitiator system may comprise 4 to 40 percent by weight of the peroxideinitiator, based on the weight of the free radical initiator system; orin the alternative, the free radical initiator system may comprise 4 to30 percent by weight of the peroxide initiator, based on the weight ofthe free radical initiator system; or in the alternative, the freeradical initiator system may comprise 10 to 40 percent by weight of theperoxide initiator, based on the weight of the free radical initiatorsystem.

The free radical initiator system further includes at least onehydrocarbon solvent. The hydrocarbon solvent may, for example, be a C₅to C₃₀ hydrocarbon solvent. Exemplary hydrocarbon solvents include, butare not limited to, mineral solvents, e.g. from mineral oils, normalparaffinic solvents, isoparaffinic solvents, cyclic solvents, and thelike. The hydrocarbon solvents may, for example, be selected from thegroup consisting of n-octane, iso-octane (2,2,4-trimethylpentane),n-dodecane, iso-dodecane (2,2,4,6,6-pentamethylheptane), and otherisoparaffinic solvents. Exemplary hydrocarbon solvents such asisoparaffinic solvents, for example, are commercially available underthe tradenames ISOPAR C, ISPOAR E, and ISOPAR H, from ExxonMobilCompany, USA. The free radical initiator system may, for example,comprise less than 99 percent by weight of the hydrocarbon solvent,based on the weight of the free radical initiator system. All individualvalues and subranges less than 99 weight percent are included herein anddisclosed herein; for example, the free radical initiator system maycomprise 5 to 95 percent by weight of the hydrocarbon solvent, based onthe weight of the free radical initiator system; or in the alternative,the free radical initiator system may comprise 5 to 90 percent by weightof the hydrocarbon solvent, based on the weight of the free radicalinitiator system; or in the alternative, the free radical initiatorsystem may comprise 10 to 90 percent by weight of the hydrocarbonsolvent, based on the weight of the free radical initiator system.

The free radical initiator system further includes a polar a co-solvent.The polar co-solvent may be an alcohol co-solvent, for example, a C₁ toC₃₀ alcohol. Additionally, the alcohol functionality of the alcoholco-solvent may, for example, be mono-functional or multi-functional.Exemplary alcohols as a polar co-solvent include, but are not limitedto, isopropanol (2-propanol), allylalcohol (1-pentanol), methanol,ethanol, propanol, butanol, 1,4-butanediol, combinations thereof,mixtures thereof, and the like. The free radical initiator system may,for example, comprise less than 80 percent by weight of the polarco-solvent, based on the weight of the free radical initiator system.All individual values and subranges less than 80 weight percent areincluded herein and disclosed herein; for example, the free radicalinitiator system may comprise 0.1 to 80 percent by weight of the polarco-solvent, based on the weight of the free radical initiator system; orin the alternative, the free radical initiator system may comprise 2 to60 percent by weight of the polar co-solvent, based on the weight of thefree radical initiator system; or in the alternative, the free radicalinitiator system may comprise 2 to 30 percent by weight of the polarco-solvent, based on the weight of the free radical initiator system; orin the alternative, the free radical initiator system may comprise 5 to15 percent by weight of the polar co-solvent, based on the weight of thefree radical initiator system.

In an alternative embodiment, the polar co-solvent may be an aldehyde.Such aldehydes are generally known to a person of skill in the art; forexample, propionaldehyde may be use as a polar co-solvent. However, thereactivity potential of aldehydes as chain transfer agents should betaken into account when using such aldehydes polar co-solvents. Suchreactivity potentials are generally known to a person of skill in theart.

In another alternative, the polar co-solvent may be a ketone. Suchketones are generally known to a person of skill in the art; forexample, acetone or tetrahydrofuran may be use as polar co-solvents.However, the reactivity potential of ketones as chain transfer agentsshould be taken into account when using such ketones polar co-solvents.Such reactivity potentials are generally known to a person of skill inthe art.

The free radical initiator system according to instant invention mayfurther include a chain transfer agent. Such chain transfer agents aregenerally known to a person of skill in the art, and they include, butare not limited to, propane, isobutane, acetone, propylene, isopropanol,butene-1, propionaldehyde, and methyl ethyl ketone (“MEK”). In thealternative, such chain transfer agent may be charged into the reactorvia a separate inlet port. In another alternative, such chain transferagents may be mixed with ethylene, pressurized, and then charged intothe reactor.

In production, the peroxide initiator may initially be dissolved ordiluted in a hydrocarbon solvent, and then the polar co-solvent may beadded to the peroxide initiator/hydrocarbon solvent mixture prior to themetering of the free radical initiator system into the polymerizationreactor. In the alternative, the peroxide initiator may initially bedissolved or diluted in a hydrocarbon solvent, and then the polarco-solvent may be added to the peroxide initiator/hydrocarbon solventmixture immediately prior to the metering of the free radical initiatorsystem into the polymerization reactor. In another alternative, theperoxide initiator may be dissolved in the hydrocarbon solvent in thepresence of the polar co-solvent.

The high pressure, free radical (co)polymerization process for producinga low density polyethylene polymer includes the steps of polymerizingethylene and optionally at least one comonomer under high pressureconditions using a free radical initiator system comprising at least oneperoxide initiator, at least one hydrocarbon solvent, and at least onepolar co-solvent. The term (co)polymerization, as used herein, refers toboth polymerization and copolymerization of ethylene.

The high pressure (co)polymerization process is generally known in theart. Generally the (co)polymerization process involves the free radicalpolymerization of ethylene gas in the presence of a liquid hydrocarbonmedium containing organic peroxide initiators. The (co)polymerizationprocess is generally conducted at elevated temperatures and pressures.The (co)polymerization may be carried out in either a batch-wise processor continuous manner. The (co)polymerization reaction may be carried outin a tubular reactor, an autoclave reactor, or a combination of atubular reactor and an autoclave reactor. Such reactors are generallyknown to a person of skill in the art. For example, a tubular reactormay have a diameter to the length ratio of 1:14,000. The tube istypically surrounded by a jacket-tube for reception of a heat transfermedium. The jacket-tube itself may be subdivided into multiple zonesoperable independently of one another. At the end of the reaction tube,there is a valve which serves to control the pressure in thepolymerization chamber, and to discharge the reaction product. Followingthis valve, there are typically a conventional high pressure separatorand a conventional low pressure separator for separating the polymerobtained from unpolymerized substances, i.e., mainly from the portion ofthe monomers which have not been involved in the (co)polymerization.

In a high pressure (co)polymerization process, ethylene may, forexample, be pressurized in a primary compressor and a secondarycompressor, and then fed into the reactor. A free radical initiatorsystem comprising at least one peroxide initiator, at least onehydrocarbon solvent, and at least one polar co-solvent is alsopressurized, and then fed into the reactor. The free radical initiatorsystem may further include a chain transfer agent; or in thealternative, a chain transfer agent may individually be pressurized andfed into the reactor. The (co)polymerization reaction is conducted atelevated temperatures and pressures. When the (co)polymerizationreaction is completed, or at a desired suitable percent conversion priorto completion, the (co)polymerization reaction may be quenched orterminated by reducing the reaction temperature. For example, the(co)polymerization reaction may be terminated by reducing the processingtemperature to below about 100° C.; or in the alternative, the(co)polymerization reaction may be terminated by reducing the processingtemperature to below about 40° C., although the exact temperaturedepends upon the specific reactants involved. Following completion ortermination of the reaction, the resultant polymer can be optionallyseparated from the reaction mixture, washed and dried. Subsequentprocessing of the polyethylene homopolymer or copolymer can then beconducted.

The (co)polymerization pressure is typically in the range of about 500to about 5000 bars. All individual values and subranges in the range ofabout 500 to about 5000 bars are included herein and disclosed herein;for example, (co)polymerization pressure is in the range of about 1200to about 4000 bars; or in the alternative, (co)polymerization pressureis in the range of about 1500 to about 3500 bars. The (co)polymerizationtemperature is typically in the range of about 70° C. to about 380° C.All individual values and subranges in the range of about 70° C. toabout 370° C. are included herein and disclosed herein; for example,(co)polymerization temperature is in the range of about 100° C. to about365° C.; or in the alternative, (co)polymerization temperature is in therange of about 120° C. to about 360° C.

Ethylene homopolymers or copolymers may be produced via a high pressurepolymerization process. The method of the present invention can be usedfor both the homopolymerization of ethylene and the copolymerization ofethylene with one or more other monomers, provided that these monomersare copolymerizable with ethylene under free-radical conditions underhigh pressure. Examples of suitable copolymerizable monomers are α,β-unsaturated C₃-C₈-carboxylic acids, in particular maleic acid, fumaricacid, itaconic acid, acrylic acid, methacrylic acid and crotonic acidderivates of the α, β-unsaturated C₃-C₈-carboxylic acids, e.g.unsaturated C₃-C₁₅-carboxylic acid esters, in particular ester ofC₁-C₆-alkanols, or anhydrides, in particular methyl methacrylate, ethylmethacrylate, n-butyl methacrylate, ter-butyl methacrylate, methylacrylate, ethyl acrylate n-butyl acrylate, 2-ethylhexyl acrylate,tert-butyl acrylate, methacrylic anhydride, maleic anhydride or itaconicanhydride, and α-olefins such as propene, 1-butene, 1-pentene, 1-hexene,1-octene, or 1-decene. Vinyl carboxylates, for example vinyl acetate,can also be used as comonomers. Exemplary comonomers include, but arenot limited to, n-butyl acrylate, acrylic acid and methacrylic acid. Theproportion of comonomer or comonomers in the reaction mixture may befrom 1 to 45 percent by weight, based on the weight of ethylene. Allindividual values and subranges in the range 1 to 45 weight percent areincluded herein and disclosed herein; for example, the proportion ofcomonomer or comonomers in the reaction mixture may be from 1 to 30percent by weight, based on the weight of ethylene; or in thealternative, the proportion of comonomer or comonomers in the reactionmixture may be from 1 to 20 percent by weight, based on the weight ofethylene. In the case of copolymerization, the further comonomers arepreferably fed in at a plurality of points along the reactor.

The (co)polymerization process according to instant invention may beemployed to produce a low density polyethylene polymer. Such polymersmay be fabricated into a variety of articles e.g. films and moldedarticles. Different methods may be employed to make such films andmolded articles. For example, a film according to the instant inventionmay be formed via blown film process or cast film process. A moldedarticle according to instant invention may be formed via injectionmolding process or extrusion coating process. Such methods are generallyknown in the art.

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicating the scope of the invention.

EXAMPLES

The following examples illustrate the present invention but are notintended to limit the scope of the invention. The examples of theinstant invention demonstrate that the free radical initiator system ofthe instant invention provides improved phase separation properties.

Experimental Setup:

The high pressure solubility tests were carried out in a high pressureoptical cell, as shown in FIG. 1, which was designed for the measurementof cloud-point pressures. In this setup, liquid-solid phases andliquid-liquid phase transitions were detected by visual observation,which was recorded by a camera.

Experimental Protocol:

The cell was filled with the mixture of components and pressurized from0 to 3500 bar at a constant temperature. The sample was agitated with amagnetic stirred while both pressure and temperature were recordedonline. The phase separation behavior of the liquid was recorded in realtime using a video camera.

Formulation Ingredients: Initiators:

-   -   (1) Luperox® JWEB50 (polyether poly-t-butylperoxycarbonate        initiator dissolved in 50 weight percent ethylbenzene),        available from Arkema; and    -   (2) Trigonox F, (tert-butyl peroxyperacetate (“TBPA”)),        available from Akzo Nobel.

Solvents:

(1) n-octane; (2) iso-octane (2,2,4-trimethylpentane); (3) n-dodecane;(4) iso-dodecane (2,2,4,6,6-pentamethylheptane); and (5) Isopar® E.

Alcohols:

(1) isopropanol (2-propanol); and (2) allylalcohol (1-pentanol)

Samples solution 1-16 were prepared according to the formulations listedon Table I, and then tested for high pressure solubility according tothe above-described Experimental Setup and Experimental Protocol inExperiments 1-6. The results are shown below and in FIGS. 2-7.

Example 1

Sample solutions 1 (comparative) and 2 (inventive), according to theformulations listed in Table I, were prepared and tested for highpressure solubility according to the above-described Experimental Setupand Experimental Protocol. The liquid-liquid phase separation is shownas a function of temperature and pressure for comparative samplesolution 1(containing 20 weight percent Luperox JWEB50 and 80 weightpercent iso-octane), and inventive sample solution 2 (containing 20weight percent Luperox JWEB50 and 10 weight percent isopropanol and 70weight percent iso-octane) in FIG. 2. Referring to FIG. 2, the graphshows that the liquid-liquid phase transition was lowered byapproximately 30 to 35° C. to lower temperatures due to the addition of10 weight percent of iso-propanol in inventive sample solution 2.

Example 2

Sample solutions 3-7, according to formulations listed in Table I, wereprepared and tested for high pressure solubility according to theabove-described Experimental Setup and Experimental Protocol. Theliquid-liquid phase separation is shown as a function of temperature andpressure for comparative sample solution 3 (containing 40 weight percentLuperox JWEB50 and 60 weight percent n-octane), inventive samplesolution 4 (containing 40 weight percent Luperox JWEB50 and 5 weightpercent isopropanol and 55 weight percent n-octane), and inventivesample solution 5 (containing 40 weight percent Luperox JWEB50 and 10weight percent isopropanol and 50 weight percent n-octane) in FIG. 3.Furthermore, the solid-liquid phase separation is shown as a function oftemperature and pressure for comparative sample solution 6 (containing100 weight percent n-octane), and inventive sample solution 7(containing 40 weight percent Luperox JWEB50 and 20 weight percentisopropanol and 40 weight percent n-octane) in FIG. 3. Referring to FIG.3, the graph shows that the addition of 5 weight percent iso-propanollowered the liquid-liquid phase transition by 15 to 20° C. to lowertemperatures; the addition of 10 weight percent iso-propanol lowered theliquid-liquid phase transition by approximately 30 to 35° C. to lowertemperatures; the addition of 20 weight percent iso-propanol preventedthe liquid-liquid phase transition, and improved the solubility untilthe solid-liquid phase transition occurs; and the addition of 20 weightpercent iso-propanol lowered the solid-liquid phase transitionapproximately 40° C. to lower temperatures.

Example 3

Sample solutions 8-9, according to formulations listed in Table I, wereprepared and tested for high pressure solubility according to theabove-described Experimental Setup and Experimental Protocol. Theliquid-liquid phase separation is shown as a function of temperature andpressure for comparative sample solution 8 (containing 40 weight percentLuperox JWEB50 and 60 weight percent Isopar E), and inventive samplesolution 9 (containing 40 weight percent Luperox JWEB50 and 5 weightpercent isopropanol and 55 weight percent Isopar E) in FIG. 4. Referringto FIG. 4, the graph shows that the addition of 5 weight percent ofisopropanol lowered the liquid-liquid phase transition approximate by 15to 20° C. to lower temperatures.

Example 4

Sample solutions 8-9, according to formulations listed in Table I, wereprepared and tested for high pressure solubility according to theabove-described Experimental Setup and Experimental Protocol. Theliquid-liquid phase separation is shown as a function of temperature andpressure for comparative sample solution 6 (containing 100 weightpercent n-octane), comparative sample solution 8 (containing 40 weightpercent Luperox JWEB50 and 60 weight percent Isopar-E), inventive samplesolution 10 (containing 40 weight percent Luperox JWEB50 and 10 weightpercent 1-pentanol and 50 weight percent n-octane) in FIG. 3. Thesolid-liquid phase separation is also shown as a function of temperatureand pressure for comparative sample solution 6 (containing 100 weightpercent n-octane), and inventive sample solution 10 (containing 40weight percent Luperox JWEB50 and 10 weight percent 1-pentanol and 50weight percent n-octane) in FIG. 5. Referring to FIG. 5, the graph showsthat at pressures below 2000 bar, the liquid-liquid phase transition islowered by approximately 35° C. to lower temperatures due to theaddition of alcohol. Furthermore, the graph shows that at above 2000bar, the solid-liquid phase transition is lowered by approximately 40°C. due to the addition of alcohol.

Example 5

Sample solutions 11-12, according to formulations listed in Table I,were prepared and tested for high pressure solubility according to theabove-described Experimental Setup and Experimental Protocol. Theliquid-liquid phase separation is shown as a function of temperature andpressure for comparative sample solution 11 (containing 20 weightpercent TBPA and 80 weight percent iso-dodecane), and inventive samplesolution 12 (containing 20 weight percent TBPA and 10 weight percentisopropanol and 70 weight percent iso-dodecane) in FIG. 6. Referring toFIG. 6, the graph shows that liquid-liquid phase transition is loweredby approximately 15 to 20° C. due to the addition of 10 weight percentof iso-propanol.

Example 6

Sample solutions 11-12, according to formulations listed in Table I,were prepared and tested for high pressure solubility according to theabove-described Experimental Setup and Experimental Protocol. Theliquid-liquid phase separation is shown as a function of temperature andpressure for comparative sample solutions 11, 13 and 14 (containing 20weight percent, 35 weight percent, and 50 weight percent TBPA iniso-dodecane, respectively), and for inventive sample solutions 12, 15and 16 (containing 20 weight percent, 35 weight percent, and 45 weightpercent TBPA with 10 weight percent isopropanol in iso-dodecane,respectively) in FIG. 7. Referring to FIG. 7, the graph shows that theliquid-liquid phase separation was lowered approximately by 15° C. tolower temperatures due to addition of isopropanol.

Referring to FIG. 8, the T-X plot for Trigonox-F is shown at 3 differentpressure levels, i.e. 500 bar, 1500 bar and 2500 bar, for comparativesample solutions 11, 13, and 14 (containing 20 weight percent, 35 weightpercent, and 50 weight percent of TBPA in iso-dodecane, respectively)and for inventive sample solutions 12, 15 and 16 (containing 20 weightpercent, 35 weight percent, and 45 weight percent TBPA with 10 weightpercent isopropanol in iso-dodecane, respectively). The T-X plot forTrigonox F shows that the liquid-liquid phase separation regions havemoved to lower temperature levels at all three pressure levels, i.e. 500bar, 1500 bar and 2500 bar, due to the presence of isopropanol.

TABLE I Initiator concentration (wt %) Solvent concentration (wt %)Alcohol concentration (wt %) Initiator Type Solvent Type Alcohol TypeSolution 1 20 wt % Luperox JWEB 50  80 wt % iso-octane None(comparative) Solution 2 20 wt % Luperox JWEB 50  70 wt % iso-octane 10wt % iso-propanol (inventive) Solution 3 40 wt % Luperox JWEB 50  60 wt% n-octane None (comparative) Solution 4 40 wt % Luperox JWEB 50  55 wt% n-octane  5 wt % iso-propanol (inventive) Solution 5 40 wt % LuperoxJWEB 50  50 wt % n-octane 10 wt % iso-propanol (inventive) Solution 6None 100 wt % n-octane None (comparative) Solution 7 40 wt % LuperoxJWEB 50  40 wt % n-octane 20 wt % iso-propanol (inventive) Solution 8 40wt % Luperox JWEB 50  60 wt % Isopar E None (comparative) Solution 9 40wt % Luperox JWEB 50  55 wt % Isopar E  5 wt % iso-propanol (inventive)Solution 10 40 wt % Luperox JWEB 50  50 wt % n-octane 10 wt % 1-pentanol(inventive) Solution 11 20 wt % Trigonox F  80 wt % iso-dodecane None(comparative) Solution 12 20 wt % Trigonox F  70 wt % iso-dodecane 10 wt% iso-propanol (inventive) Solution 13 35 wt % Trigonox F  65 wt %iso-dodecane None (comparative) Solution 14 50 wt % Trigonox F  50 wt %iso-dodecane None (comparative) Solution 15 35 wt % Trigonox F  55 wt %iso-dodecane 10 wt % iso-propanol (inventive) Solution 16 45 wt %Trigonox F  45 wt % iso-dodecane 10 wt % iso-propanol (inventive)

1. A high pressure, free-radical polymerization process for producing alow density polyethylene polymer comprising the steps of: polymerizingethylene and optionally at least one comonomer under high pressureconditions using a free radical initiator system comprising at least oneperoxide initiator, at least one hydrocarbon solvent, and at least onepolar co-solvent, wherein said polar co-solvent is one or more C₁ to C₃₀alcohols.
 2. The high pressure, free-radical polymerization process forproducing a low density polyethylene polymer according to claim 1,wherein said peroxide initiator is an organic peroxide initiator.
 3. Thehigh pressure, free-radical polymerization process for producing a lowdensity polyethylene polymer according to claim 1, wherein saidhydrocarbon solvent is a C₅ to C₃₀ hydrocarbon solvent.
 4. The highpressure, free-radical polymerization process for producing a lowdensity polyethylene polymer according to claim 1, wherein saidhydrocarbon solvent is a solvent selected from the group consisting ofmineral solvents, normal paraffinic solvents, isoparaffinic solvents,cyclic solvents, and the like.
 5. The high pressure, free-radicalpolymerization process for producing a low density polyethylene polymeraccording to claim 1, wherein said hydrocarbon solvent is a solventselected from the group consisting of n-octane, iso-octane(2,2,4-trimethylpentane), n-dodecane, iso-dodecane(2,2,4,6,6-pentamethylheptane), and isoparaffin.
 6. The high pressure,free-radical polymerization process for producing a low densitypolyethylene polymer according to claim 1, wherein said alcohol is amono-functional or multi-functional alcohol.
 7. The high pressure,free-radical polymerization process for producing a low densitypolyethylene polymer according to claim 1, wherein said alcohol is aco-solvent selected from the group consisting of isopropanol(2-propanol), allylalcohol (1-pentanol), methanol, ethanol, propanol,butanol, and 1,4-butanediol.
 8. The high pressure, free-radicalpolymerization process for producing a low density polyethylene polymeraccording to claim 1, wherein said free radical initiator systemcomprises 2 to 30 percent by weight of said alcohol based on the weightof said system.
 9. The high pressure, free-radical polymerizationprocess for producing a low density polyethylene polymer according toclaim 1, wherein said free radical initiator system comprises 5 to 15percent by weight of said alcohol based on the weight of said system.10. The high pressure, free-radical polymerization process for producinga low density polyethylene polymer according to claim 1, wherein saidfree radical initiator system comprises 5 to 95 percent by weight ofsaid hydrocarbon solvent based on the weight of said system.
 11. Thehigh pressure, free-radical polymerization process for producing a lowdensity polyethylene polymer according to claim 1, wherein said freeradical initiator system comprises 1 to 40 percent by weight of saidperoxide initiator based on the weight of said system.
 12. The highpressure, free-radical polymerization process for producing a lowdensity polyethylene polymer according to claim 1, wherein said freeradical initiator system comprises 4 to 30 percent by weight of saidperoxide initiator based on the weight of said system.
 13. A low densitypolyethylene polymer produced via process of claim
 1. 14. A film, amolded product, or an extrusion coated product prepared from the lowdensity polyethylene of claim
 13. 15-30. (canceled)
 31. A method ofimproving the metering of a peroxide initiator into a high pressurereactor for producing a low density polyethylene polymer comprising thesteps of: polymerizing ethylene and optionally at least one comonomerunder high pressure conditions using a free radical initiator systemcomprising at least one peroxide initiator, at least one hydrocarbonsolvent, and at least one polar co-solvent, wherein said polarco-solvent is one or more C₁ to C₃₀ alcohols.